Vulcan was a small island located just off the coast of Sicily in Italy on Earth. It apparently had dry weather.
A hologram of Leonardo da Vinci noted that a "fascinating" conversation with Tuvok had left him "as dry as Vulcan". Tuvok, initially taken aback by the simile (as the location's name was the same as his homeworld's), replied that he had never been there when asked. (VOY: "Concerning Flight")